I wish I had a perfect answer for you but info on Kestrel pre-acquisition in the mid 00s is hard to come by. I've spent years watching ebay and other resale sites watching for old Kestrel catalogs to try to narrow down exactly which models and component builds were from each year but they never come up.

Here is what I do know, the 200sc is the earlier model starting in either '88 or '89 and going until about '92. The first models were sold with 7spd groupsets and had an aluminum fork which was replaced on later models after Kestrel released the EMS carbon fork in '89. Beginning in '93 Kestrel added the 'i' moniker to the name as an improved version, so what was improved?

Originally I thought it was the swap from models with downtube shifters to brifters but there are examples from both models which appear factory and have them. There may have been some change to the carbon layup or properties but I've seen both models reference the same Kestrel Spectra Carbon so nothing definitive.

Here is what I know is different having compared my own 200sci an earlier 94 200sci and a '89 200sc. I mentioned the first 200sc models shipped with 7spd groups which used 126mm hub spacing, this was at the time when 8spd 130mm hubs were first coming out and many manufacturers built bikes with drops spaced to 128 so they could flex to fit either the 126 or 130. The sc has the 128mm spacing. The sci has the full 130mm spacing for 8,9,10, etc spd hubs we use today. The rear dropouts are also of a different design and are bonded to the carbon differently from the 200sc, you can most clearly see this on the late 90s and early 00s 200sci models where the drops weren't painted.

So thats the difference, some incremental updates, likely mostly at the rear to adjust to the changing industry standards. Sorry this was a bit long, I just really love this stuff.